1. Field of the Invention
The present invention relates to the field of structuring of substrates, and more particularly without limitation, to semi-conductor and micromachined devices.
2. Background and Prior Art
Microchip manufacturing relies on photolithography, a process similar to photography, to define the shape and pattern of individual surface features. A film of photo-reactive polymer, known as a photoresist, is applied to the surface of a silicon wafer where a latent image is generated in the photoresist by exposure to light.
Photolithography can also be used for producing a three dimensional topography. For this purpose several photolithographic steps have to be performed in a sequence. The difficulty with two or more layers of topography is that the layer alignment is difficult to achieve. This difficulty limits the precision of the structuring of the substrate. As a consequence certain structures such as lenses having a defined focal point can to date not be produced by means of photolithographic multilayer processes.
Another field of application of photolithography is micromachining of miniature mechanical or other devices. It is a particular challenge for such applications to produce steps, slopes or other surface variations. The ability to coat the substrate with a uniform thickness of photo resist has been identified as one of the toughest challenges in the area of pattern definition for high topography structures (cf. SPIE Micromachining & Microfabrication Symposium '96, “Imaging and Resist Technologies for the Micromachining Industry”, David Craven).
There is therefore a need for providing of an improved method of structuring of a substrate, in particular for producing miniature steps, slopes or other surface variations of the substrate and for semiconductor manufacturing.